1. Field of the Invention
This invention relates to an air motor for using a dental hand-piece and the like, more particularly to an air motor comprising an air turbine supported by axle-bearings mounted on both ends of the air turbine shaft in the motor body of the air motor, wherein compressed air-flow introduced from the end portion of the motor body is supplied through an air charging passage formed within the same body to jet the compressed air into the turbine chamber, thereafter exhaust air discharged from the turbine chamber is further exhausted to outside through an exhaust air discharging passage formed within the same body.
2. Description of the Prior Art
Conventionally such a turbine type air motor is used for a dental hand-piece or another cutting tool of fine work and the like. In case of dental hand-piece, for example, an air motor comprising a collet mounted on one end of hand-piece body to fit a cutting tool with the collet and also an air turbine directly connected with the collet, and compressed air-flow introduced from the rear end of the hand-piece body is then charged into a turbine chamber through an air charging passage formed within the hand-piece body. After the compressed air-flow used in the turbine chamber gives a rotating energy to the air turbine, the discharged air from the turbine chamber is passed so as to be turned back through the exhaust air discharging passage formed within the motor body, wherein the exhaust air is then exhausted to outside from a exhaust port located in a middle position or rear portion of the motor body. The above conventional air turbine, which is connected with the collet, is then rotated in a state so that the both ends of turbine shaft are supported by two pieces of the axle-bearings and thus the rotation frequency of air turbine reaches approximately 200,000 to 300,000 r.p.m. (revolutions per minute).
As a disadvantage of such conventional air turbine, however, due to this high frequency for the turbine rotation, the axle-bearings of supporting the turbine shaft inevitably generate frictional heat, consequently the life of axle-bearing is rapidly shortened if no heat radiation is provided to the bearing portion.